This invention relates to controlling a valve that discharges a fluid while dispensing a dosage of an additive to the fluid in proportion to the quantity of fluid. The invention particularly relates to a method and apparatus that utilize a mechanical memory for accumulating information as to the quantity of the fluid and using that accumulated information to trigger the dispensing of the additive.
There are many situations in which it is necessary to dispense a controlled dosage of an additive into a quantity of a fluid in preset proportions. One such situation involves roof top water reservoirs that are used to provide a desired water pressure within a building. The contents of the reservoirs are typically open to the atmosphere to prevent creation of a vacuum in the reservoir. However, the fact that they are open to the atmosphere makes the water susceptible to bacteria and algae growth. This problem is typically eliminated by the regular addition of a controlled quantity of a bactericidal chemical such as chlorine to the water.
Prior approaches to controlling the concentration of the bactericidal chemical in the water have involved measuring the flow of water added to the reservoir and dispensing an appropriate quantity of the chemical based upon the measured volume of water. However, flow measuring devices are expensive and trouble prone and are not suitable for measuring relatively small flow rates.
One more recent approach is described in commonly owned, co-pending application Ser. No. 783,297 filed Oct. 2, 1985 by Paul R. Goudy, Jr., et al. for Bactericidal Mixture Control System. In that approach, flow of the water into the reservoir is initiated by a float actuated switch and the duration of the flow is controlled. While the water flow is occuring, a dispenser dispenses chemical into the reservoir according to a preset dispensing cycle which is initiated when the water flow is initiated and also terminates when the water flow terminates.
The present invention represents an approach for controlling the concentration of an additive into a fluid, such as water in an open reservoir, by controlling the duration during which valves are open to discharge the fluid into the reservoir and by accumulating information concerning the duration of discharge in a simple but efficient mechanical memory which triggers the dispensing of the additive into the fluid in the reservoir in preselected proportions to the amount of fluid added to the reservoir.